Prior Art Systems Using Vortex Tubes
Vortex tubes, such as those provided by Exair Corporation, come in a variety of sizes and models and are known to those of ordinary skill in the art of providing cooling, or alternately heating, capability to electronic and other operations.
A prior art system utilizing vortex tubes for cooling, and/or heating, of an enclosure includes U.S. Pat. No. 6,401,463 to Dukhan, et al. Dukhan teaches the use of a vortex tube with a system of chambers for simultaneous heating of one chamber of an enclosure containing battery components and cooling of another chamber of the enclosure containing other electronic components. Dukhan teaches the use of a vortex tube's output via a manifold to direct air onto specific components within an enclosure with the directed air passing into ambient air within the enclosure to help control ambient temperature in which a plurality of components function under normal operating conditions.
Another prior art system teaches the use of vortex tubes for cooling of components in a data storage system as shown in U.S. Pat. No. 7,751,188 to French et al. French teaches the use of one or more vortex tubes to generate and direct cold air over heat-generating components of an electronic system in a data storage cabinet. Hot exhaust from the vortex tube system is ducted from the cabinet to the ceiling through a chimney-like duct. As shown in FIG. 5 of the French patent, the system disclosed in French also uses a manifold to split and direct cold air output from a vortex tube to individualized electronic devices, such as CPUs. Thus, French is directed to the use of a vortex tube to direct air into cold air plates having within them radially extending fins, or baffling, for directing the cold air output from the vortex tube directly onto and over the surface of a CPU, the directed air then passing out through openings in the cold plates into ambient air within the cabinet to help control the ambient temperature in which a plurality of components function under normal operating conditions.
U.S. Pat. No. 7,263,836 to Gunawardana et al. teaches the use of a vortex tube to cool one or more components within a cooling chamber. The vortex tube is powered by a compressor that receives air from both the hot air outlet of the vortex tube and used air from the cooling chamber. A series of pressurized chambers and valves function in a closed-loop system to maintain the ambient operating temperature for electronics in the cooling chamber at appropriate operating temperatures.
None of the aforementioned systems has involved the application of vortex tubes for thermal control of testing of integrated circuits in the open where humans routinely occupy the same space as testing fixtures. Rather each has been applied within a cabinet, enclosure or data storage room not intended for frequent and consistent worker presence. Such testing in an open environment requires that extreme cold and hot air temperatures and noise generated during tests be prevented from unduly impacting workers in the test environment. Accordingly, none of the aforementioned systems has addressed the specific issues encountered in a testing-oriented thermal control scenario, such as the need for noise abatement while achieving rapid cooling and heating setpoint device temperatures, the need for rapidly heating and then cooling a single specific device in an enclosure, or the need for accurately cycling a device under test through a relatively wide range of setpoint temperatures in stepped sequence while testing and recording data for each chip tested.
Occupational Health Safety Administration standard 1910.95(a) for Occupational Noise Exposure, specifies that a worker may be exposed to a maximum noise level of 90 decibels (dBA) for a period of eight hours. Without a muffler, a single typical vortex tube operates at a noise level of over 100 decibels (dBA). With a typical muffler, a single vortex tube operates at a noise level of approximately 80-88 decibels (dBA). For a worker to be able to work around a plurality of simultaneously and continuously operating vortex tubes, the noise level of each vortex tube in operation would require significant noise reduction from existing levels to be safe for workers.
Prior art methods of employing a heatsink to cool electronic components have involved the use of a combination thermoelectric cooling device, a fan, or other cooler, together with a heatsink shroud for directing air from the fan over the heatsink, or vice versa for enhancing the cooling of the heatsink by removing heated air from the heatsink. Examples of such patents include U.S. Pat. No. 6,515,862 to Wong et al., for Heatsink Assembly For An Integrated Circuit; U.S. Pat. No. 6,637,502 to North et al., for Heatsink With Converging Device; and U.S. Pat. No. 6,876,550 to Sri-Jayantha et al., for Heatsink For High Power Microprocessors. None of these heatsink, fan and shroud type patents involve the use of fans and heatsinks in a testing environment for use for ramping a device under test (DUT) up or down to a temperature extreme for testing purposes.
Prior Art Thermal Control of Integrated Circuit Tests
It is highly desirable to test newly manufactured integrated circuits over a fairly wide range of operating temperatures on the order of −40° C. to 125° C., or in some cases even a wider range of temperatures between −55° C. to 150° C. Such testing enables a manufacturer to determine temperature extremes at which a chip will operate to in turn enable the manufacturer to certify that the chip is able to be operated at rated temperatures. This, in turn, determines to a degree the value of the chip in the marketplace and the types of applications for which the chip is suitable.
A typical integrated circuit test environment requires cycling rate requirements of a range of 0.3° C. to 2° C./second in a hot ramp to a hot setpoint, and a range of 0.2° C. to 0.5° C./second in a cold ramp to a cold setpoint.
Prior art methods of air-supplied temperature control for testing environments include fan-assisted heatsink assemblies, pressurized ambient air blown directly, or indirectly, onto a heatsink, housing or onto a device under test, or air supplied to an integrated heatsink and housing with, or without, assistance from one or more thermoelectric coolers and/or fans. The use of pressurized air and fan systems in a testing environment is noisy, requiring ear protection for workers working in that environment.
Other methods of controlling temperature of test equipment include liquid coolant assisted heatsink assemblies. While water and other liquid coolants provide a satisfactory means of heating and cooling test fixtures, a problem with these devices is that at very cold temperatures, standard coolants tend to freeze. Alternate low-temperature coolants have been developed to deal with this problem, but they require special system components and are expensive. Also, since, liquids are corrosive and otherwise damaging to electronic components, there is a need to control the liquid with specialized apparatus and to monitor for leakages.
The lower ends of the required rate requirement ranges mentioned above correspond to normal bench top rates of about 300 seconds to attain −40° C. from 25° C. ambient, and similarly to 125° C. for hot ramp. The faster rate requirements mentioned above represent maximum values desirable in high repetitive cycling testing applications.
These maximum value ramp rates are not as conveniently attainable with prior art methods of thermal control requiring liquid thermal control systems which must account for and prevent corrosion to parts, condensation, freezing and the like.
Thermal control of such testing environments has required control of the temperature of the Integrated Circuits (ICs), sensor and other test elements, since variables in a DUT temperature can be introduced by an inability to precisely control the application of heat or cold to the DUT. As a practical matter, such testing normally occurs to a DUT within a testing socket, requiring that heat or cold being applied to the DUT also affects the temperature of the socket. Further, operation of the DUT during the test also generates a significant amount of heat. Thus, there is a need to control the amount of the heat/cooling applied to the DUT from and external source relative to the internal heat generated during operation of the DUT.
The use of heaters and/or coolers applied to a heatsink thermally connected with a DUT is not new. U.S. Pat. No. 7,187,189 to Lopez et al. teaches the use of a heater applied to a heatsink to control the temperature of a DUT similar to that of U.S. Pat. Nos. 5,164,661 and 5,420,521 to Jones.
Apparatus for cooling a DUT for test applications has included liquid coolants or forced air, using fans or air compression means, applied to a heatsink apparatus contacting the DUT. These apparatus have in some cases further comprised the use of one or more integrated thermoelectric coolers. Forced air, such as with fans or compressors, have also been used to apply the air stream directly to the DUT surface to be cooled during testing.
None of these patents or prior art methods discloses the use of output air from a vortex tube to cool or heat a DUT to the types of temperatures and in the time frames important to a successful production chip testing environment.
More accurate test results have been able to be performed by more accurately controlling the temperature of the DUT. Prior art methods of heating and cooling chips, for example in an oven without individual temperature control, have led to variable temperature characteristics for the device under test as a result of heat dissipation, radiation or convection within the oven and among the testing components in the oven.
Thus, there have been developed means of individually sensing, predicting and controlling temperature in individual IC test sockets as shown and described in U.S. Pat. No. 7,394,271 to Lopez et al.
Under normal circumstances operation of a vortex tube with normal ambient air temperature input has been capable of producing temperatures ranging from −46° C. to 127° C. In some testing applications to test components under extremely cold or extremely hot conditions it would be desirable to have colder temperatures, or hotter temperatures, than those of normal vortex tube capability with ambient air inputs. While it is known generally that a vortex tube will produce colder output based upon colder input, or hotter output based upon hotter input, specific methods of accomplishing pre-cooling or pre-heating suitable to a thermal control system for testing or other application to which the present invention is directed have not been disclosed.
Accordingly, while there has developed a need and ability to accurately and quickly control, stepwise transitioning of temperatures of individual ICs under a wide range of temperature test conditions, there has been lacking in the prior art an efficient and accurate method of heating and cooling individual ICs with pressurized air in a way that hasn't unduly impacted testing personnel with excessive noise, temperature or other undesirable chemical or other properties.